A variety of different heat transfer systems use water or other fluids to transfer heat or thermal energy between one or more production units and one or more loads. Such systems are often referred to as hydronic systems.
Many such systems employ variable pumping in which the speed of the pumps or number of active pumps is varied to maintain a constant pressure cross some terminal, sometimes referred to as the “index circuit.” The logic of choosing this circuit is to provide sufficient pressure to all circuits by providing enough pressure to the circuit with the most demanding needs. The disadvantage to this approach is that the circuit with the greatest need does not remain constant. Some circuits might need more pressure than others, but initially have enough pressure as a result of their location within the network. As the total flow in the distribution system decreases and the pressure difference between the risers in various locations equalizes, such circuits would become the most demanding.